In the field of medical electrical systems, it is often desirable to utilize a minimum number of implanted medical electrical leads, each including as many electrodes and/or physiological sensors as are feasible. It is further desirable to reduce the number of connections between each lead and an implanted device in order to reduce bulk in a subcutaneous pocket where the device resides.
Medical electrical lead connectors and the mating connector ports of devices have been standardized in the industry; examples of standards for cardiac therapy include the IS-1 standard, for low voltage applications, i.e. pacing, and the DF-1 standard, for high-voltage applications, i.e. defibrillation. Other contemplated standards define connections for both high-voltage and low-voltage with a single device connector port and a single lead connector in order to achieve a lower profile system.
Clinical experience has shown that, in some patients, an acceptable defibrillation threshold cannot be reached using two high-voltage electrodes located on a single lead. In other patients, a chronic energy requirement for effective defibrillation may increase due to worsening heart condition or a change in medication. For these patients, it becomes necessary to implant, either at the time of original device implantation or after that time, another defibrillation electrode in order to create an effective vector for the delivery of defibrillation energy.
Furthermore it is contemplated that two low voltage electrodes located on a single lead may not meet the long term therapeutic goals for an implanted system, for example to provide cardiac resynchronization, and that, in these cases, an additional pacing electrode should be added to the system.
For the aforementioned cases, along with others in the broader field of medical electrical systems, it is desirable to provide means for augmenting a medical electrical system without adding an additional device connector port.